The present invention relates to a device for controlling an acceleration pump for a carburetor.
When the opening degree of a throttle valve is suddenly changed from a small one to a large one in order to accelerate the engine speed, air is promptly supplied into the engine cylinder, but fuel is not supplied into it in proportion thereto because a part of the fuel is adhered onto an induction passage wall so that the fuel cannot be sufficiently supplied into the engine. Thus, the air-fuel mixture becomes tentatively lean.
For such a reason, the engine cannot be promptly accelerated even if the throttle valve is widely opened. To solve this problem, an acceleration device is provided to supply an increased volume of fuel when the throttle valve is suddenly opened to a large extent.
FIG. 1 shows a conventional acceleration device which is a piston type acceleration pump. A carburetor body 1 has an induction passage P wherein a throttle valve 2 is arranged. A piston 3 in the acceleration pump is made of metal or the like. When throttle valve 2 opens, a throttle lever 4 rotates together with the throttle valve 2 so that a connecting rod 5 moves upwardly whereby a pump lever 7 rotates around a shaft 6 counterclockwise. As a result, the right end of the pump lever 7 moves up while the left end thereof moves down so that the piston 3 moves down against the biasing force of a return spring 8. When the opening degree of the throttle valve 2 becomes small, the piston 3 returns to its original position by the biasing force of the return spring 8.
When the piston 3 moves up, the fuel 10 in a float chamber 9 opens an inlet valve 11 so that the fuel flows into a cylinder 12. When the piston 3 again moves down, that is, when the throttle valve 2 is opened to a large extent, the fuel within the cylinder 12 opens an outlet valve 13 so that the fuel can be supplied through a pump nozzle 14 into the induction passage P upstream of the throttle valve 2.
According to the opening degree of the throttle valve 2, a rate of supplying the fuel into the engine is controlled so as to obtain good acceleration characteristics.
In such a conventional acceleration device, however, only one rate of supplying the fuel is predetermined so as to be matched to the air density under the standard atmospheric pressure. Therefore, it is not matched to another air density, for example, at a high place such as a mountain. Although the density of the air supplied into the engine is small at a high place, the same increased fuel is supplied thereinto. Thus, the air-fuel mixture becomes too rich. As a result, fuel consumption worsens, and exhausted noxious substances such as HC, CO cannot be easily disposed.